Enzyme Chemistry Introduction
At the chemical level, living things keep living because they contain protein
molecules called enzymes that are able to control the chemical reactions that
occur in living cells. The exercises that can be done with the kit components
investigate two different enzymes. One enzyme is called salivary amylase
because it is found in saliva and it digests starch (amylose). The other enzyme is
called catalase and it speeds up the breakdown of hydrogen peroxide, a
potentially toxic compound called an oxidant. Catalase is found in most living
tissues, but it is especially concentrated in liver tissue. For the perspective of
student understanding, the action of salivary amylase is more accessible
because most students grasp the concept that somehow the food we eat is
broken down in our digestive tracts. However, the reaction of hydrogen peroxide
with a small piece of beef or chicken liver is much more dramatic, producing
oxygen gas which displaces the syringe in the same way that carbon dioxide did
when vinegar was added to baking soda.
The write-ups included here investigate salivary amylase (although you don’t
want to start by giving it this name). If you would rather use catalase instead of
or in addition to salivary amylase, the second write-up involves catalase reaction
(where H202 is broken down into water and oxygen). You can also have students
bubble the resulting gas through BTB to reinforce that not all reactions produce
the same type of gas (CO2).
Extensions:
The enzyme exercises can be excellent ways to introduce the topic of digestion.
If you can get some cellophane dialysis tubing (Carolina Biological Supply
Company -- $14.00 for a 50 ft. roll), this can be used to illustrate a variety of
additional concepts such as the size of molecules (“big” molecules like starch
cannot diffuse through the cellophane membrane, while “small” molecules like
iodine can). Therefore, if a bag is filled with starch and placed in water
containing iodine, the iodine will diffuse into the bag turning the starch blue. If
you can obtain some glucose test strips from a pharmacy, you can have students
spit into a bag containing starch and later find glucose outside the bag after the
starch is broken down, thus allowing students to investigate what actually
happens in the digestive system.
Materials/Costs:
All of these biochemistry labs use the materials in the basic science kit
mentioned in the Is It Alive? set of labs. (about $100 for everything) The only
additional costs would be for cheesecloth, mortars and pestles (if used),
hydrogen peroxide, starch solutions, fresh iodine solution, and fresh liver
samples.
WHAT HAPPENS TO STARCH WHEN IT IS MIXED WITH SALIVA?
Most of you probably know that saliva mixes with you food as you chew it. But
what does saliva do to food? One of the major components of many foods is
starch. In today’s lab, you will try to determine what effect saliva has on starch.
To do this, you will use a chemical reaction between starch and iodine which
makes starch visible by changing its color.
Materials:
Potato slices
Apple slices
Iodine solution
Droppers
50 cc reaction tubes with caps
Petri dishes
Starch solution
Begin your investigation as follows. Potatoes are considered to be a good
source of starch. Apples are believed to contain less starch. Obtain a slice of
potato and a slice of apple place them in a dish or on a piece of paper towel.
Using the dropper and the iodine solution, place a few drops of iodine solution on
each slice. What do you observe?
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Assuming that potatoes really do contain more starch than apples, what does
your observation tell you about the reaction of iodine with starch?
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Now, add starch solution to each of two reaction tubes until both tubes are filled
up to the “10” mark. Add the same number of drops of iodine solution to each
tube. What do you observe?
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Next, carefully add some of your own saliva to one of the two tubes containing
the starch-iodine mixture. Your teacher will show you how to do this. After you
have added the saliva to one of the tubes, gently swirl both the tubes for several
minutes (you may need to do this for 5 or 10 minutes) and observe any changes.
What did you observe?
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Based on your observations, what effect do you think that saliva has on starch?
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Now, you are ready to do a second lab with starch and enzymes.
THE BREAKDOWN OF STARCH BY SALIVA
You have observed that starch turns dark blue when an iodine solution is added
to the starch. You have also observed that saliva causes the blue color to
disappear when it is added to a mixture of starch and iodine. Scientists believe
the color disappears because saliva contains a factor that breaks down (i.e.
digests) starch. If this explanation is correct, perhaps the factor in saliva that
breaks down starch might be affected by temperature. Today, you will design
some experiments to test the hypothesis that the breakdown of starch by
something in saliva is affected by temperature.
1a. What is the question you are trying to answer?
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1b. What are the variables involved?
Manipulated variable
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Responding variable
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Controlled variables
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1c. What do you think will happen?
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Use the materials listed below to conduct your experiment.
Room temperature water
Ice water
Water at body temperature (37oC)
Boiling water
Soluble starch solutions
Iodine solution
Test tubes
Thermometers
Timers
2. Using the materials listed above, design an experiment to answer your
question. Describe as much detail and as many steps as you can. Write the
steps in order so they make sense.
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Note: Begin each experiment by adding saliva to one test tube and allowing the
tube to reach the temperature you are testing before you add any starch or iodine
to that test tube. In your lab write-up, you will need to make a graph which
shows any relationship that you discover between temperature and the time it
takes starch to break down.
3a. Do the experiment that you have designed in #2. Write down any
observations you make below and then construct a table to chart to record your
data.
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3b. State a hypothesis. Recall that a hypothesis is frequently stated “If the
(manipulated variable) is changed, then the (responding variable) will change in
a certain way.
Hypothesis:
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4. Use the data from your chart or table to make a graph. Remember which
variable is graphed on the x-axis and which one on the y-axis — be sure to label
the axes. Make your graph accordingly. Use the graph paper provided.
5. Using data from your chart and graph, discuss the relationship between the
manipulated and responding variable such that you can make conclusions about
how temperature and the breakdown of starch by saliva are related to each
other.
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This lab covers Colorado Model Content Standards for Science 1, 2.2, 2.3,
3.1,3.2, 3.3 & 6.
This lab covers Colorado Model Content Standards for Mathematics 3, 5, & 6.
WHAT HAPPENS WHEN HYDROGEN
PEROXIDE IS ADDED TO LIVER TISSUE?
Hydrogen peroxide (H202) is an oxidizing agent. The solution of hydrogen
peroxide that you can buy in a drug store or grocery store is used as a
disinfectant because it can kill bacteria. In this lab, you are going to explore what
happens when some hydrogen peroxide solution is added to a reaction vessel
which contains some liver tissue. Begin by doing the following experiment:
1. Obtain 2 reaction tubes, two rubber stoppers, and two 60 cc syringes.
2. Place a small piece of liver tissue (about the size of a bean) in the bottom of
one
of the tubes. Place the rubber stoppers in both tubes.
3. Take up 5 ml of hydrogen peroxide solution each of the syringes.
4. Carefully insert the tip of each syringe into the stoppers so that the hole is
closed
tightly.
5. Push down the plungers of the syringes so that the hydrogen peroxide
solution is
injected into each reaction tube.
Describe the results of the experiment. Do you think that a chemical reaction
occurred when the hydrogen peroxide was added to the liver? Why or why not?
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Now do the following experiment:
1. Remove the stopper from the reaction tube containing the liver. Pour the
liquid into a
sample cup, being careful not to transfer any visible pieces of liver into the
cup.
2. Using an empty syringe, take up the liquid from the cup into the syringe.
3. Place a fresh piece of liver in another reaction tube, put in the stopper, and
inject
the liquid from step two into the reaction tube.
Write down a description of the result:
4. Now place a stopper in the reaction tube from step #I which still contains the
original
piece of liver. Take up 5 ml of fresh hydrogen peroxide with a syringe and
inject it
into the reaction tube as you did in your original experiment. Write down a
description of the result.
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5. Repeat the procedure you did in steps 1 - 4 again using the same piece of
liver that
you used in your first experiment. Write down a description of the results.
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Now consider the following hypothesis and decide whether or not the results you
have
obtained so far support this hypothesis:
“Liver tissue contains something which can break down hydrogen peroxide,
but is not used up when this reaction occurs.”
Do your results support this hypothesis? ___________ Why or why not?
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If the hypothesis above is true, then it should be possible to find out some
additional things about the “liver factor” that may cause hydrogen peroxide to
break down. Using the materials you already have and those listed below see
what you can discover about this hypothetical “liver factor”. Carefully write down
the procedures you follow and the results. You will have to include accurate
information in your final report.
1a. What is the question you are trying to answer?
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1b. What are the variables involved?
Manipulated variable
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Responding variable
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Controlled variables
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1c. What do you think will happen?
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Use the materials below to conduct your experiment:
Gas collectors
Liver
Mortars and pestles*
Cheesecloth
Boiling water baths
Reaction tubes and reaction tube holders*
Strongly acidic solutions*
Strongly basic solutions *
Ice
BTB
Other animal and plant tissues
Balance or scale to weigh
*Exercise can be done without these, but it helps to have them. Plastic cups can
be substituted for test tubes.
2. Experimental design: Write the steps in order and in as much detail as
possible.
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3a. Conduct the experiment that you have designed. Write down special
observations below and make a chart or table to record your data.
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Table or chart:
3b. State your hypothesis:
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4. Use your data from the table or chart to make a graph. Graph paper will be
provided.
5. Using data you have collected and analyzed, write a discussion of your
findings. Be sure to include information about how your variables interacted and
affected with other.
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This lab covers Colorado Model Content Standards for Science 1, 2.2, 2.3,
3.1,3.2, 3.3 & 6.
This lab covers Colorado Model Content Standards for Mathematics 3, 5, & 6.